Devices such as User Equipments (UE) are also known as e.g. mobile terminals, wireless terminals and/or mobile stations. Devices are enabled to communicate wirelessly in a wireless communications system or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two devices, between a device and a regular telephone and/or between a device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications system.
Devices may further be referred to as mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as device or a server.
The wireless communications system covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the devices within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for devices. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP GSM EDGE Radio Access Network (GERAN), a device has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. EDGE is an abbreviation for Enhanced Data rates for GSM Evolution. In the end of 2008 the first release, Release 8, of the 3GPP Long Term Evolution (LTE) standard was finalized and later releases have also been finalized.
Recent developments of the 3GPP LTE facilitate accessing local Internet Protocol (IP) based services in the home, office, public hot spot or even outdoor environments. One of the important use cases for the local IP access and local connectivity involves the direct communication between devices in close proximity, typically less than a few 10 s of meters, but sometimes up to a few hundred meters of each other.
In network-controlled so-called Device-to-Device (D2D) communications, a network such as a radio access network assists devices that are in the proximity of each other to discover one another, in a process referred to as device discovery, and establish a direct link referred to as D2D bearer establishment, rather than a link via the base station. In fact, when two devices communicate with each other via a cellular base station, the communication path involves an uplink hop and a downlink hop, both with associated resources, as opposed to the single hop direct D2D link. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station or device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station or communication device to the base station.
The initiation of the establishment of the D2D link may be made by the radio access network or by any of the devices of the D2D pair. In network initiated D2D link establishment, the network realizes that two communicating devices are in proximity of each other. In device initiated D2D link establishment, the devices discover the proximity of each other and also some of their capabilities which is necessary for them to establish a D2D link, similar to Bluetooth.
In network-controlled D2D communication, a network control function performs at least one of: a) provisioning of a discovery signal to be used between two devices to determine their proximity and/or D2D link estimation, b) resource assignment for the D2D discovery signal and/or a D2D data channel and/or a D2D control channel, c) relaying of information between the at least two devices, and d) configuration of connection parameters for the at least two devices of the D2D link, such as power setting, e.g., actual, min, max, coding and modulation schemes, segmentation configuration, e.g., transport block sizes, parameters and/or security keys for encryption/integrity protection and protocol parameters.
A transmission in an LTE or Evolved Universal Terrestrial Radio Access Network (E-UTRAN) is based on Orthogonal Frequency Division Multiplexing (OFDM), whose format may be modeled as an OFDM time-frequency grid. The OFDM time-frequency grid is comprised in one axis of frequency values and in the other axis of time. The frequency axis is subdivided in a number of frequency sub-carriers, with a spacing that may typically correspond to 15 kHz, while the time axis is subdivided in OFDM symbol intervals.
Within the grid, a Physical Resource Block (PRB or RB) is a unit of transmission resource consisting of twelve consecutive sub-carriers in the frequency domain and one time slot, 0.5 ms, in the time domain.
The direct communication mode, or D2D communication, enables a number of potential gains over the traditional cellular technique, because D2D devices are much closer to one another than cellular devices that have to communicate via a cellular access point, e.g., a base station:                Capacity gain: First, radio resources, e.g., OFDM RB, between the D2D and cellular layers may be reused, i.e., reuse gain. Second, a D2D link uses a single hop between the transmitter and receiver points as opposed to the 2-hop link via a cellular access point, i.e., hop gain.        Peak rate gain: due to the proximity and potentially favorable propagation conditions, modulation and coding scheme (MCS) of higher order may be applied, so that, the maximum achievable data rate may be further improved, i.e., proximity gain;        Latency gain: When the devices communicate over a direct link, the base station forwarding is short cut and the end-to-end latency may decrease.        
In a mixed cellular and D2D network resulting from the coexistence of these two systems, the Physical layer (PHY) channel design has to take into account the inter-system interference, i.e., interference between cellular sub-system and D2D sub-system. The coexistence of the systems may result in two types of interference: 1) co-channel or co-RB interference, i.e., interference on the same RB; and 2) inter-channel or inter-RB interference due to in-band emission, i.e., the interference from allocated RB to un-allocated RBs within the band. Here a band may be defined as a continuous frequency range (3GPP defined multiple bands in 3GPP TS 36.101, EUTRA User Equipment (UE) radio transmission and reception, 2012.03), and a corresponding carrier frequency is a specific frequency that is used to carry the radio signal which spans the whole frequency band.
As shown by the following table defined by 3GPP (3GPP TS 36.101, EUTRA User Equipment (UE) radio transmission and reception, 2012.03), the in-band emission, i.e., the interference from allocated RBs to un-allocated RBs within the band, is restricted to different levels for different cases, depending on the specific value of the system bandwidth, allocated RB size, Error Vector Magnitude (EVM), transmission power, etc. First, for a general case, i.e., when the measurement bandwidth is 1 RB and the limit is expressed as a ratio of measured power in one non-allocated RB to the measured average power per allocated RB, where the averaging is done across all allocated RBs. Second, for an image frequencies case, i.e., when the applicable frequencies for this limit are those that are enclosed in the reflection of the allocated bandwidth, based on symmetry with respect to the center carrier frequency, but excluding any allocated RBs. And third, for a carrier frequency leakage case, i.e., when the applicable frequencies for this limit are those that are enclosed in the RBs containing or adjacent to the DC frequency, but excluding any allocated RB.
TABLE 1In-band Emission formulaParameterdescriptionUnitLimit (Note 1)Applicable FrequenciesGeneraldBmax {−25 − 10 · log10(NRB/LCRBs),Any non-allocated (Note 2)20 · log10 EVM −3 − 5 · (|ΔRB|−1)/LCRBs,−57 dBm/180 kHz − PRB}IQ ImagedB−25Image frequencies (Notes 2, 3)CarrierdBc−25Output power >0 dBmCarrier frequency (Notes 4, 5)leakage−20−30 dBm ≦ Output power ≦0 dBm−10−40 dBm ≦ Output power <−30 dBm
Where NRB is defined as the transmission bandwidth configuration, expressed in units of resource blocks, LCRBs is defined as the length of a contiguous resource block allocation, |ΔRB| is defined as the starting frequency offset between the allocated RB and the measured non-allocated RB, PRB is defined as the transmitted power per 180 kHz in allocated RBs, measured in dBm. A simple calculation may be as follows: For a general item, given a 5 MHz bandwidth, 5 RBs allocated to a cellular device, whose transmission signalling EVM=0.175, Tx power=23 dBm, then the in-band emission would be I=max[−32, −18−x, −57], where x is the starting frequency offset between the allocated RB and the measured non-allocated RB, e.g., x=0 for the first adjacent RB outside of the allocated bandwidth, x=1 for the second, i.e., an emission from −18˜−32 dB would be caused. This emission would be more serious for more allocated RB size, RBs most next to the allocated RB, larger EVM. As shown in FIG. 1, even if a −30 dB emission is assumed, a nearby cellular device, e.g., 10 m, would cause failure of D2D communication on neighboring band. According to International Mobile Telecommunications-Advanced (IMT-A) Indoor Non-Line of Sight (NLOS), path loss model: 43.3*log 10(10 m)+11.5+20*log 10(2 GHz)=60.82 dB.
Thus, co-channel and/or inter-channel interference is a problem in a mixed wireless network.